1. Field of the Invention
This invention relates to improved vanes or blades of a gas turbine engine, particularly an improved foil cap therefor.
2. The Prior Art
In the high operating temperatures of gas turbine engines sufficient gas cooling of foils, including vane and/or blade surfaces is important if not essential. The prior art has expended considerable effort in cooling designs for such vanes and blades located, e.g. aft of the engine combustion chamber. Generally in the prior art, cooling gas, e.g. air, is directed into a hollow vane or blade and through apertures in the walls thereof, which apertures are, e.g. slanted and flared to lay down a cooling gas film on the vane or blade exterior surfaces, to provide a cooling gas film layer thereon against the oncoming combustion core gas stream.
For examples of such vane or blade cooling efforts see U.S. Pat. No. 3,527,543 to Howald (1970), U.S. Pat. No. 4,197,443 to Sidenstick (1980), U.S. Pat. No. 4,589,823 to Koffel (1986) and U.S. Pat. No. 4,650,949 to Field (1987).
The above references teach forming cooling apertures through the walls of vanes or blades at an angle with the exterior surface thereof employing cylindrical apertures (Koffel), conical apertures (Howald) or apertures which flare at the exit end thereof (Sidenstick and Field). These references teach cooling of the sidewalls of the respective vanes and blades but do not address cooling of the cap end of, e.g. vanes, particularly (inwardly) cantilevered vanes, where core gas flow over the vane ends or root caps is desirably minimized while trying to preserve a cooling film thereover.
The cantilevered vanes are mounted, e.g. in a gas turbine engine supported outwardly and cantilevered inwardly and around an adjustable core body, known as an active clearance control, ACC, which can expand to close the gap therebetween to minimize the flow of engine core gases over the root caps and direct such flow between the vanes.
That is, in the prior art, cantilevered vane 10 has sidewall cooling apertures 12, with no apertures for the upper surfaces of the root cap 14, which is subject to oxidation and/or erosion caused by core gas contacting same, as indicated in FIG. 5.
In another example of the prior art, shown in FIG. 6, cantilevered vane 20 works in conjunction with active clearance control member (ACC) 22, which moves into contact with the upper surfaces 24 of the vane 20 so as to block core gas flow over the vane ends or root cap to thus reduce gas turbine performance (power and efficiency) losses and to direct such core gas flow between the vanes 20 as much as possible.
However, when the ACC 22 closes on the end 24 of the root cap 23, it seals off the cooling apertures 26 of the vane 20 and overheating of such cap results which can lead to oxidation and/or erosion thereof, unless the operating temperatures of the engine are significantly reduced, at the expense of efficiency and power thereof.
Accordingly, there is need and market for a foil cap for gas turbine blades and vanes, including cantilevered vanes, which can obviate the above prior art shortcomings.
There has now been discovered an improved foil cap design for gas turbine blades and cantilevered vanes which permits cooling of such caps even when an engine member is in contact therewith, for improved engine efficiency and higher operating temperatures.